Flask



FIG. 1 is a perspective top view showing the new design for the flask.

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof.

The broken lines are included for the purpose of illustrating a portion of the flask that forms no part of the claimed design. 

CLAIM The ornamental design for a flask, as shown and described. 